Method for producing  a cylinder for a two-stroke engine and casting core therefor

ABSTRACT

The invention relates to a method for producing a cylinder ( 10, 110 ) for a two-stroke engine, comprising the following steps: producing a casting core ( 30, 130 ), wherein a central core slide ( 31, 131 ) for the cylinder chamber ( 11, 111 ) and at least one salt core ( 33, 133 ) for an overflow channel ( 18, 19; 118, 119 ) are produced and the at least one salt core ( 33, 133 ) is connected to the central core slide ( 31, 131 ), inserting the casting core ( 30, 130 ) into a casting mold, casting the cylinder ( 10, 110 ) in a die-casting process, removing the central core slide ( 31, 131 ) from the cylinder ( 10, 110 ), wherein the at least one salt core ( 33, 133 ) is separated from the central core slide ( 31, 131 ), and flushing the at least one salt core ( 33, 133 ) out of the cylinder ( 10, 110 ). The invention further relates to a casting core ( 30, 130 ) for such a method.

The present invention relates to a method for the production of a cylinder for a two-stroke engine as well as to a casting core for this method.

Such cylinders are generally cast from an aluminum alloy, in a gravity casting method, using sand cores. It is problematic, in this connection, that casting defects and inclusions form very easily. For this reason, it is aimed at to cast such cylinders in a die-casting method. However, sand cores cannot be used for this, because they do not withstand the pressure conditions that prevail during casting.

DE 33 31 664 A1 describes a cylinder having closed overflow channels for a two-stroke engine, which is produced using the die-casting method. Divided steel cores are used to form the overflow channels; these cores are connected with the central core slide for the cylinder chamber. Both the configuration of the multi-part cores and the removal of the divided steel cores for the overflow channels from the cast cylinder are very complicated and difficult.

It is furthermore known to use cores made of a wood fiber material (cf. DE 198 20 246 A1). However, such cores have not proven themselves for the die-casting method, because they are not sufficiently stable for it.

The task of the present invention consists in further developing a method of the stated type and a casting core of the stated type, in such a manner that the casting core can easily be removed from the cast cylinder, and is also suitable for a die-casting method.

The solution consists in that first, a casting core is produced, whereby a central core slide for the cylinder chamber and at least one salt core for an overflow channel are produced, and the at least one salt core is connected with the central core slide, that the casting core is subsequently introduced into a casting mold, and the cylinder is cast using a die-casting method, that subsequently, the central core slide is removed from the cylinder, whereby the at least one salt core is separated from the central core slide, and finally, the at least one salt core is flushed out of the cylinder.

The casting core according to the invention is characterized in that it has a central core slide for the cylinder chamber, to which at least one salt core for an overflow channel is connected.

It has turned out, in surprising manner for a person skilled in the art, that a salt core connected with a central core slide is so stable that it withstands the conditions, particularly the pressure conditions, of a die-casting method. The at least one salt core can be flushed out of the cast cylinder particularly easily, in known manner. The method according to the invention and the casting core according to the invention therefore make it possible to produce cylinders for two-stroke engines, which have at least one overflow channel, with little effort, using the die-casting method.

Advantageous further developments are evident from the dependent claims.

The at least one salt core can be produced in known manner, by means of pressing, injection-molding, or also by means of sintering. Sodium chloride and/or potassium chloride, for example, are suitable as main components. If necessary, at least one binder can be added, for example at least one alkali carbonate and/or at least one earth alkali carbonate.

The central core slide can be produced from various desired materials. Metallic materials, particularly steel materials, are preferred.

The at least one salt core is preferably connected with the central core slide with shape fit and without binders.

The method according to the invention and the casting core according to the invention are particularly suitable for the production of cylinders that are cast from an aluminum alloy, using a die-casting method.

Exemplary embodiments of the present invention will be explained in greater detail below, using the attached drawings. These show, in a schematic representation, not true to scale:

FIG. 1 an exemplary overall representation of a cylinder for a two-stroke engine, in section;

FIG. 2 a cylinder for a two-stroke engine, with a first exemplary embodiment, situated in it, of a casting core according to the invention, in section;

FIG. 3 the cylinder according to FIG. 1, after removal of the casting core;

FIG. 4 another exemplary overall representation of a casting core according to the invention, in a perspective, slanted view;

FIG. 5 the casting core according to FIG. 4 in a front view;

FIG. 6 another cylinder for a two-stroke engine, in section, produced with a casting core according to FIGS. 4 and 5;

FIG. 7 a section along the line VII-VII in FIG. 6.

FIG. 1 shows a schematic representation of a cylinder 10 for a two-stroke engine. In the exemplary embodiment, a piston-edge-controlled two-stroke engine is shown, as it is used, for example, for hand tools such as power saws. Such a two-stroke engine has at least one cylinder 10 having a cylinder chamber 11, in which a piston 12, which has a piston crown 16, is guided to move up and down. The cylinder 10 is closed off by a cylinder head 13 at one end. The other end of the cylinder 10 is attached to a crankcase 14, which is only shown in outlines in FIG. 1. The piston 12 is connected, in known manner, by means of a piston pin and a connecting rod, with a crankshaft that is mounted to rotate in the crankcase 14 (not shown).

In the cylinder 10, a combustion chamber 15 is formed, which is delimited by the cylinder head 13, the piston crown 16 of the piston 12, and the cylinder wall 17 of the cylinder chamber 11. In the exemplary embodiment, an overflow channel 18 is shown, which connects the combustion chamber 15 with the crankcase 14. The cylinder chamber 11 furthermore has an outlet channel 21 for conducting away the combustion gases that occur, out of the combustion chamber 15. Below the opening of the overflow channel 18 into the combustion chamber 15, the cylinder chamber 11 furthermore has an inlet channel 22, by way of which a fuel/air mixture is introduced into the crankcase 14. The outlet channel 21, the inlet channel 22, and the opening of the overflow channel into the combustion chamber 15 are opened and closed by the piston 12, which is moving up and down, as a function of its stroke position.

In the position of the piston 12 shown in FIG. 1, in the region of its lower dead center, the outlet channel 21 and the opening of the overflow channel 18 into the combustion chamber 15 are open. In this position, the fuel/air mixture compressed by the piston 12 in the crankcase flows into the combustion chamber 15 (see arrow S) and displaces the combustion gases situated the combustion chamber 15, which exit from the combustion chamber 15 by way of the outlet channel 21. During the following upward movement of the piston 12 in the direction toward the cylinder head 13, first the opening of the overflow channel 18 into the combustion chamber 15 is closed, and subsequently the outlet channel 21 is closed. At the same time, the inlet channel 22 is opened, so that fresh fuel/air mixture is drawn into the crankcase 14. The piston 12 compresses the fuel/air mixture situated in the combustion chamber 15 on its path to the upper dead center, until it ignites below the combustion chamber roof 23 formed by the cylinder head 13. During the subsequent downward stroke, the inlet channel 22 is closed, and the fresh fuel/air mixture drawn into the crankcase 14 is compressed. Then, first the outlet channel 22 and subsequently the opening of the overflow channel 18 into the fuel chamber 15 are opened, and the work cycle begins anew.

FIGS. 2 and 3 show an exemplary embodiment of the present invention in a simplified representation. FIG. 2 shows a cylinder 10 for a two-stroke engine composed of an aluminum alloy. The cylinder 10 was cast in known manner, using a die-casting method.

The casting core 30 according to the invention used for this purpose has a central core slide 31 and a foot plate 32 provided on it. The core slide 31 serves for forming the cylinder chamber 11. The foot plate 32 essentially serves to close off the casting mold and to pull the core slide 31 out of the cast cylinder 10, in the direction of the arrows A, after casting. The core slide 31 and the foot plate 32 consist, in the exemplary embodiment, of the steel material X37CrMoV5-1 hardened to 48-52 HRC.

In the exemplary embodiment, two salt cores 33 are connected with the core slide 31; these serve to form two overflow channels 18, 19. The salt cores 33 consist, in the exemplary embodiment, of pressed sodium chloride or of pressed potassium chloride.

Connecting the salt cores 33 to the core slide takes place by means of a shape-fit connection.

The salt cores 33 support themselves on the foot plate 32 in the exemplary embodiment. The finished casting core 30 is laid into a casting mold. The cylinder 10 is cast from an aluminum material, using a die-casting method.

When the core slide 31 is pulled out after casting of the cylinder 10, the salt cores 33 are sheared off from the core slide 31 or separated from the foot plate 32. The salt cores 33 are not flushed out of the cylinder 10 in known manner, so that two overflow channels 18, 19 result. The support of the salt cores 33 on the foot plate 32 brings about the result that the overflow channels each have an opening 18 a, 19 a in the direction of the crankcase to be added later. After the crankcase is added, the overflow channels open into the crankcase.

FIGS. 4 to 7 show another exemplary embodiment of a cylinder 110 produced according to the method according to the invention, and of a casting core 130 used for this purpose. The cylinder 110 has a cylinder chamber 111, two overflow channels 118, 119, an outlet channel 121, and an inlet channel 122. The casting core 130 has a core slide 131 made from a steel material, particularly from heat-treated steel X37CrMoV5-1 hardened to 48-52 HRC, for forming the cylinder chamber 111. Two salt cores 133 for forming the overflow channels 118, 119 are connected with the core slide 131. Furthermore, a mold part 121 a for forming an outlet channel 121 and a mold part 122 a for forming an inlet channel 122 are provided on the central core slide 131. 

1. Method for the production of a cylinder (10, 110) for a two-stroke engine, having the following method steps: production of a casting core (30, 130), wherein a central core slide (31, 131) for the cylinder chamber (11, 111) and at least one salt core (33, 133) for an overflow channel (18, 19; 118, 119) are produced, and the at least one salt core (33, 133) is connected with the central core slide (31, 131), introduction of the casting core (30, 130) into a casting mold, casting of the cylinder (10, 110) using a die-casting method, removal of the central core slide (31, 131) from the cylinder (10, 110), wherein the at least one salt core (33, 133) is separated from the central core slide (31, 131), flushing of the at least one salt core (33, 133) out of the cylinder (10, 110).
 2. Method according to claim 1, wherein the at least one salt core (33, 133) is pressed.
 3. Method according to claim 1, wherein the at least one salt core (33, 133) is sintered.
 4. Method according to claim 1, wherein the at least one salt core (33, 133) is produced using the injection-molding method.
 5. Method according to claim 1, wherein the at least one salt core (33, 133) is produced from sodium chloride as the main component.
 6. Method according to claim 1, wherein the at least one salt core (33, 133) is produced from potassium chloride as the main component.
 7. Method according to claim 1, wherein the at least one salt core (33, 133) is produced using at least one alkali carbonate and/or at least one earth alkali carbonate.
 8. Method according to claim 1, wherein the central core slide (31, 131) is produced from a steel material.
 9. Method according to claim 1, wherein the cylinder (10, 110) is cast from an aluminum alloy.
 10. Casting core (30, 130) for the production of a cylinder (10, 110) for a two-stroke engine, having a central core slide (31, 131) for the cylinder chamber (11, 111), wherein at least one salt core (33, 133) for an overflow channel (18, 19; 118, 119) is connected with the central core slide (31, 131).
 11. Casting core according to claim 10, wherein the at least one salt core (33, 133) is pressed.
 12. Casting core according to claim 10, wherein the at least one salt core (33, 133) is sintered.
 13. Casting core according to claim 10, wherein the at least one salt core (33, 133) is produced using the injection-molding method.
 14. Casting core according to claim 10, wherein the at least one salt core (33, 133) consists of sodium chloride as the main component.
 15. Casting core according to claim 10, wherein the at least one salt core (33, 133) consists of potassium chloride as the main component.
 16. Casting core according to claim 10, wherein the at least one salt core (33, 133) contains at least one alkali carbonate and/or at least one earth alkali carbonate.
 17. Casting core according to claim 10, wherein the central core slide (31, 131) consists of a steel material. 